Implement generic Double and related fixed types

Added :class:`.Double`, :class:`.DOUBLE`, :class:`.DOUBLE_PRECISION`
datatypes to the base ``sqlalchemy.`` module namespace, for explicit use of
double/double precision as well as generic "double" datatypes. Use
:class:`.Double` for generic support that will resolve to DOUBLE/DOUBLE
PRECISION/FLOAT as needed for different backends.

Implemented DDL and reflection support for ``FLOAT`` datatypes which
include an explicit "binary_precision" value. Using the Oracle-specific
:class:`_oracle.FLOAT` datatype, the new parameter
:paramref:`_oracle.FLOAT.binary_precision` may be specified which will
render Oracle's precision for floating point types directly. This value is
interpreted during reflection. Upon reflecting back a ``FLOAT`` datatype,
the datatype returned is one of :class:`_types.DOUBLE_PRECISION` for a
``FLOAT`` for a precision of 126 (this is also Oracle's default precision
for ``FLOAT``), :class:`_types.REAL` for a precision of 63, and
:class:`_oracle.FLOAT` for a custom precision, as per Oracle documentation.

As part of this change, the generic :paramref:`_sqltypes.Float.precision`
value is explicitly rejected when generating DDL for Oracle, as this
precision cannot be accurately converted to "binary precision"; instead, an
error message encourages the use of
:meth:`_sqltypes.TypeEngine.with_variant` so that Oracle's specific form of
precision may be chosen exactly. This is a backwards-incompatible change in
behavior, as the previous "precision" value was silently ignored for
Oracle.

Fixes: #5465
Closes: #7674
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/7674
Pull-request-sha: 5c68419e5aee2e27bf21a8ac9eb5950d196c77e5

Change-Id: I831f4af3ee3b23fde02e8f6393c83e23dd7cd34d

2 files changed, 9 insertions, 9 deletions

diff --git a/lib/sqlalchemy/testing/suite/test_reflection.py b/lib/sqlalchemy/testing/suite/test_reflection.py
index 6f02d5557..fb12d23c8 100644
--- a/lib/sqlalchemy/testing/suite/test_reflection.py
+++ b/lib/sqlalchemy/testing/suite/test_reflection.py
@@ -344,7 +344,7 @@ class ComponentReflectionTest(fixtures.TablesTest):
                 metadata,
                 Column("user_id", sa.INT, primary_key=True),
                 Column("test1", sa.CHAR(5), nullable=False),
-                Column("test2", sa.Float(5), nullable=False),
+                Column("test2", sa.Float(), nullable=False),
                 Column(
                     "parent_user_id",
                     sa.Integer,
@@ -361,7 +361,7 @@ class ComponentReflectionTest(fixtures.TablesTest):
                 metadata,
                 Column("user_id", sa.INT, primary_key=True),
                 Column("test1", sa.CHAR(5), nullable=False),
-                Column("test2", sa.Float(5), nullable=False),
+                Column("test2", sa.Float(), nullable=False),
                 schema=schema,
                 test_needs_fk=True,
             )
diff --git a/lib/sqlalchemy/testing/suite/test_types.py b/lib/sqlalchemy/testing/suite/test_types.py
index 94bab009a..0940eab9b 100644
--- a/lib/sqlalchemy/testing/suite/test_types.py
+++ b/lib/sqlalchemy/testing/suite/test_types.py
@@ -731,7 +731,7 @@ class NumericTest(_LiteralRoundTripFixture, fixtures.TestBase):
 
     def test_render_literal_float(self, literal_round_trip):
         literal_round_trip(
-            Float(4),
+            Float(),
             [15.7563, decimal.Decimal("15.7563")],
             [15.7563],
             filter_=lambda n: n is not None and round(n, 5) or None,
@@ -783,17 +783,17 @@ class NumericTest(_LiteralRoundTripFixture, fixtures.TestBase):
     @testing.requires.floats_to_four_decimals
     def test_float_as_decimal(self, do_numeric_test):
         do_numeric_test(
-            Float(precision=8, asdecimal=True),
-            [15.7563, decimal.Decimal("15.7563"), None],
-            [decimal.Decimal("15.7563"), None],
+            Float(asdecimal=True),
+            [15.756, decimal.Decimal("15.756"), None],
+            [decimal.Decimal("15.756"), None],
             filter_=lambda n: n is not None and round(n, 4) or None,
         )
 
     def test_float_as_float(self, do_numeric_test):
         do_numeric_test(
-            Float(precision=8),
-            [15.7563, decimal.Decimal("15.7563")],
-            [15.7563],
+            Float(),
+            [15.756, decimal.Decimal("15.756")],
+            [15.756],
             filter_=lambda n: n is not None and round(n, 5) or None,
         )